528 T. Holm — Ceanothus Americanus and ovatus. 



swellings on the lateral roots ; they are unbranched and are 

 much thicker than the normal ones. Their epidermis is simply 

 papillose, and there is no exodermis. The cortex consists of 

 five peripheral strata of normal structure, and of six internal, 

 the cells of which are very large, stretched radially and filled 

 with the fungus. The endodermis is like that of the main 

 root and free from fungus. A pericambium surrounds five 

 groups of leptome and a central, confluent mass of hadrome. 



The primary root persists and represents a long, woody 

 taproot in old specimens, reaching a thickness of about l cm or 

 even a little more ; such old roots are generally of a reddish 

 brown color due to the cell-contents of the peripheral strata of 

 the cortex. Another peculiarity possessed by the mature 

 root is the presence of sclerotic cells, which occur in. groups 

 in the secondary cortex. Otherwise the mature root shows the 

 same structure as observed in younger specimens, with a very 

 pronounced, excentric growth of the hadrome and the medul- 

 lary rays. 



The leaves. — The cotyledons (fig. 2) have stomata on both 

 faces of the blade ; these are surrounded by several cells, from 

 four to seven, none of which are parallel with the stoma. 

 The stomata are most numerous on the dorsal face of the 

 blade. The chlorenchyma is differentiated into a typical pali- 

 sade-tissue and an open pneumatic tissue of roundish or oblong, 

 loosely connected cells. An almost colorless parenchyma- 

 sheath surrounds the very thin mestome-strands, which have 

 no support of stereomatic or collenchymatic tissues. 



The petioles of the cotyledons have no chlorenchyma, but a. 

 large tissue of colorless cells which surrounds two separate, 

 broad mestome-strands. The cuticle is wrinkled and epidermis 

 quite thick-walled. A layer of collenchyma separates epidermis 

 from the colorless tissue, in which a few, two to three, muci- 

 lage-cells are located. 



In a mature leaf from a flower-bearing shoot we meet with 

 the same bifacial structure as observed in the cotyledons, but 

 the stomata are here confined to the dorsal face. The cuticle 

 is quite thick and prominently wrinkled ; the outer cell-wall 

 of epidermis is moderately thickened where it covers the veins,, 

 and hairs are quite numerous. They are of two kinds: uni- 

 and pluri-cellular, thick-walled, with the apex pointed and more 

 or less curved. The pluri-cellular hairs (of several cells in a 

 single row) occur above and below the larger veins, and out- 

 side the pneumatic tissue. The chlorenchyma consists of two 

 to three layers of palisades on the ventral face of the blade,, 

 and of four to five strata of open, pneumatic tissue on the dorsal. 



A thin-walled, colorless parenchyma surrounds the larger 

 veins ; it consists of about three strata above, but of six below 

 these, and is separated from epidermis by collenchyma.. 



